1. Field of the Invention
The present invention relates to highly molecular-oriented pulp-like short fibers prepared from liquid crystal polyesters, taking advantage of the unique properties of a melt liquid crystal phase, without a substantial spinning process.
2. Description of the Prior Art
Generally, various processes, comprising forming a melt liquid crystal phase by heating a liquid crystal polyester, and then spinning the resulting melt liquid crystal phase to produce fibers, are well known. In such spinning processes, the spinning step wherein a fiber shape is formed by passing the melt liquid crystal phase through microholes is essentially required as well as a drawing step wherein constituent molecular chains are arranged in parallel with the fiber axis must be followed so that fibers having a molecular orientation can be produced.
Recently, it has been known that some of aromatic polyesters form a liquid crystal phase which is optically anisotropic in melt state. See, for instance, U.S. Pat. Nos. 3,637,595; 3,759,870; 3,778,410; 3,804,805; 3,991,013; 4,066,620; 4,067,852; 4,075,262; 4,083,829; 4,118,372; 4,130,545; 4,140,846; 4,161,470; 4,181,792; 4,183,895; 4,184,996; 4,188,476; 4,219,461; 4,256,624; 4,318,841; 4,431,770; 4,330,4657; 4,370,466; and 4,473,682. It has also been known that in a liquid crystal phase, molecules orient spontaneously, and constituent molecular chains are easily oriented in the direction of shear even by small shear force; see Polymer Liquid Crystals, edited by A. Ciferr;, W. R. Krigbaum and R. B. Meyer, Academic Press, 1982, pp 247-273. It has, therefore, been known that if the liquid crystal polyesters are subjected to spinning, long fibers having high strength and high modulus of elasticity can be produced; see, for instance, U.S. Pat. Nos. 3,975,487; 4,159,365; 4,503,105; 4,574,066; and 4,500,696; Japanese Patent Application KoKai Nos. 131020/1983; 159816/1982; 191219/1983; 49257/1984; 78232/1984; 113818/1986; and 238821/1987. In processes for the production of fibers employing a spinning process, melt liquid crystal has to pass through microholes. It is, therefore, difficult to produce fibers using polymers having high molecular weight or high viscosity, and long post-treatment at high temperature is required after spinning. In addition, since relatively high temperature is required during the spinning, the possibility of thermal decomposition is high. For these reasons, processes for the production of fibers by spinning are expensive, and thus, the price of fibers is high. Moreover, these fibers are in the form of a long bar that has a regular shape and a uniform surface. Therefore, unlike pulp which can have various shapes and surfaces, these fibers have only limited thickness and surface area.